Can one man be CEO of two companies? Nissan and Renault are about to find out.

(FORTUNE Magazine) – RUNNING A GLOBAL CAR COMPANY ISN'T AN EASY JOB. YOU'VE got to deal with hundreds of suppliers, thousands of employees, millions of customers, and a network of factories that produces tens of millions of dollars' worth of vehicles a day. Throw in labor battles, brutal competition, and fickle consumer tastes--even if you're the most successful auto executive on the planet, you wouldn't want to think about doing much else. You certainly wouldn't want to run a second car company.

But you're not Carlos Ghosn, the 50-year-old CEO of Nissan. On April 29, Ghosn (hard "g"; rhymes with "cone") is expected to be named president and CEO of Nissan's French partner, Renault, and to add a home in Paris to the one he already has in Tokyo. It's as if Bill Belichick decided to add the San Francisco 49ers to his duties as coach of the New England Patriots and split his time between them on Sundays.

Nobody has ever tried a double dip like this in the auto industry before. Sure, Jürgen Schrempp of DaimlerChrysler oversees two companies, but he does it from 30,000 feet and under one corporate umbrella. Ghosn will be managing Renault, the world's tenth-largest automaker, and Nissan, the ninth-largest, in which Renault owns a 44% stake, as the chief executive officer of each.

It would be hard to pick a less geographically favorable situation. The two companies are separated by 9,771 miles and eight time zones (not to mention different languages, cultures, and histories). Ghosn expects to spend 40% of his time in Paris, 40% in Tokyo, and 20% in the U.S. and the rest of the world. Given his leadership style--he likes to walk factory floors, meet suppliers, visit with dealers, and do all the other flesh-pressing tasks that can't be done via teleconference--he has to pull off a flawless triple gainer of concentration and stamina that may be a stretch even for him. And that doesn't include his extracurriculars: He's on the boards of Sony, IBM, and Alcoa.

Geography and time aren't the only obstacles Ghosn faces: There's also the potential for clashes between the two jobs. It's easy to imagine a decision--say, whether to merge the two companies--that would benefit one company's shareholders over the other's. "What is perfectly good for Renault may not be perfectly good for Nissan," says Michael Useem, director of the Wharton School's Center for Leadership and Change Management. "Unless he has a Chinese wall in his cerebral cortex, he may have difficulty keeping the interests of the two companies completely separate."

But Ghosn has made a career out of exceeding expectations. Moving to Nissan in 1999 from Renault, where he was executive vice president, he transformed a directionless, debt-ridden company into one of the most dynamic and profitable automakers in the world. Ghosn accomplished this in a famously opaque culture without being able to speak Japanese. Nissan's sales continue to grow, its designs and new products are widely admired, and the beetle-browed Ghosn has become a worldwide automotive icon. In Japan, he's literally a comic-book hero.

Lucky for Ghosn, Renault won't require the same bumper-to-bumper overhaul Nissan did. Renault needs a tune-up. Under the direction of chairman and CEO Louis Schweitzer since 1992, the company has gotten lean, reduced its ties to the French government (whose ownership stake has declined from 80% in 1985 to 16% now), and become the single most popular car brand in Western Europe. Its lines of low- and medium-priced cars are both functional and stylish. Renault has also expanded internationally with the start of operations in Brazil in 1996 and South Korea in 2000. Schweitzer shrewdly acquired a stake in Nissan in 1999 and sent Ghosn to run it. Ghosn was so successful that last year Nissan contributed $2.3 billion to Renault's bottom line--about 50% of its profits.

THE HARDEST PART OF GHOSN'S WORK at Renault may be changing the corporate culture. A decade ago Ghosn described Renault as a company that put "a premium on fine phrases and arcane knowledge," held "discussions about everything and nothing," and believed "that you can't always have high productivity and high morale at the same time." He has upgraded his opinion since, but Renault still needs a shakeup. It has to enter new markets more aggressively and develop new top-of-the-line models where earlier ones failed. Renault is still very dependent on Europe, which accounts for 72% of its sales, and hasn't sold a car in the U.S.--the world's most profitable market--for more than a decade. "Unless Renault comes up with real winners," says Garel Rhys, a professor of automotive economics at the University of Cardiff Business School in Wales, "it will be very difficult to get the kind of margins that Ghosn got at Nissan."

Ghosn plans to tread more carefully than he did at Nissan, where he overturned years of tradition by laying off workers, severing ties with suppliers, and selling stakes in outside companies. "Renault today is a healthy company with a good vision and good strategy, so I think when you talk about turning it upside down, it's not very realistic," he told FORTUNE recently. "I want to rediscover the company, review what are the opportunities, what are the risks, what are the strengths, and try to see very clearly where the company is. The culture is different, the company is different, the markets we compete in are different, so the challenges are going to be different."

Those feelings of unfamiliarity are, well, familiar. "In Lebanon, I was peculiar because I was born in Brazil and spoke Portuguese," he wrote in his autobiography. "Then I went to France, and I was peculiar there too. I've always been someone who was different." At least in France there isn't the total cultural disconnect he felt when he arrived in Japan, where he couldn't even decipher Nissan's org charts. He figured he had a fifty-fifty chance of succeeding.

Ghosn's perpetual role as the Boss from Beyond is unusual for CEOs, who usually rise to the top because they are perceived as regular guys who embody the shared values of an organization. What enables Ghosn to thrive in those situations is his no-nonsense manner and his lack of guile. A man of numbers and facts, he communicates with precision and wants everything measured, quantified, and benchmarked. At Nissan, Ghosn got in the habit of announcing the company had exceeded its targets, only to set some new, even more aggressive targets that would be duly exceeded the following year.

Ghosn got little sympathy last year when he struggled to shore up one of his pet projects. When Nissan was still losing billions of dollars early in his tenure, Ghosn said he wanted to erect a second assembly plant in the U.S. to build high- margin pickup trucks, SUVs, and minivans. When he did, he broke every rule of automotive production. Assembly plants are complex organisms where thousands of things can go wrong, so production experts try to limit the number of variables when they start up a new one. Not Ghosn. He built the plant in Canton, Miss., a state with no auto industry or supplier network to speak of, staffed it with 5,800 mostly inexperienced workers, and launched it with four all-new vehicles: the Titan pickup truck, Armada and QX56 SUVs, and the Quest minivan.

The biggest headache turned out to be the first vehicle off the line, the Quest. Nissan had never built a minivan before, and with curved body panels that needed to be welded together, the Quest proved particularly troublesome. When J.D. Power published its survey of new-vehicle quality last April, defects in the Quest and other Canton-built vehicles pushed Nissan's quality ratings into the basement down there with the Kias and Land Rovers. Once strong performers, Nissan vehicles sank to 33rd place on a list of 38 brands, from 21st place the year before. It finished as high as No. 8 in the 1998 survey.

Nissan sales were still brisk, but the Power numbers were an embarrassment. Ghosn took quick action. He uprooted 220 manufacturing and product engineers from their jobs in Japan and the U.S. and organized them into SWAT teams. Then he dispatched them to supplier plants and Nissan's technical center in Michigan, as well as to Mississippi, to hunt down the quality problems and stamp them out. The results of their work won't be known until J.D. Power publishes its findings for 2005 next month. Ghosn says the problems have been corrected, and he stubbornly defends his decision to start up production in a greenfield plant with so many new products. "I think five years down the road, people will say something unique has been done at Canton."

Ghosn pays special attention to the U.S., because he considers it the most demanding consumer market in the world: open, highly competitive, and fast-moving. He immersed himself in it for the first time while running North American operations for Michelin in the early 1990s, and his impression hasn't changed. "In the U.S., we do things fast," he says. "We need to encourage people to take initiatives, look at the problems very quickly, and make sure they make the decision. You can't stay on problems, because you have to move quickly."

Months before the Canton plant problems arose, Ghosn had put himself in charge of North American operations. That meant taking on additional public duties like speechmaking and handshaking, as well as leading a daylong meeting every month. With the CEO hanging around, disputes between the U.S. and Japan were resolved in a heartbeat. Traditionally, Nissan has distributed hot-selling cars in Japan first, forcing the U.S. to wait. Last winter dealers complained to North American sales and marketing boss Jed Connelly that they couldn't get any 350Z convertibles for the spring selling season because Japan was keeping them all. Ghosn heard the complaints and got involved, and topless Z cars soon started flowing to the U.S.

IF YOU'RE A DATA SPONGE who wants to speed up your organization, you book a flight to Bentonville, Ark., to visit the masters. Nobody does hyperkinetic commerce like Wal-Mart, and Ghosn has lately taken a special interest in the world's largest company. He has had a firsthand look at how it makes decisions and handles all that merchandise with such incredible efficiency. He visited Wal-Mart CEO Lee Scott--who says he'd like to recruit Ghosn to his board someday--and sat in on merchandising and planning sessions. Now Ghosn is anxious to quantify what he has learned by benchmarking Wal-Mart's operations in purchasing, transportation, and logistics. "CEOs need from time to time to put themselves in a very different situation," says Ghosn, "where they see different companies from a different angle."

This pragmatic approach isn't common in the auto industry. Car companies sometimes build cars because they like them. Ghosn believes they should build cars that make money. That means he's willing to forgo, at least temporarily, glam technologies. For example, Nissan has lagged behind Toyota and Honda in hybrid-powered cars because Ghosn insists that the additional value in lower fuel consumption and reduced emissions is less than the extra cost. Ditto with fuel cells. Ghosn figures a car powered by fuel cells would cost about $800,000, a number that will have to be reduced by 95% before it is marketable.

Ghosn's interventions have paid off big-time. The quality problems in Mississippi made little impact on Nissan's U.S. results last year. Despite a disappointing performance by Quest, Nissan's sales jumped 24.1% in a flat market, more than twice as much as Toyota's, the next most successful manufacturer. The Altima ranked as one of the dozen most popular vehicles in America, with sales of 235,889 units. The Mississippi-built Titan pickup truck invaded a segment that the Big Three has dominated for decades, and still recorded sales of 83,848 in its first full year of production. With restyled versions of the Xterra sport utility and the Frontier compact pickup truck arriving at dealers in 2005, Nissan expects to see sales rise another 5% to 10% this year.

Ghosn's strategy is to keep pushing those sales. In May 2002 he set a goal for Nissan to raise its annual worldwide sales by one million cars, to 3.6 million, by September 2005. For North America, Ghosn targeted 300,000 additional sales, then added another 60,000 when other regions of the world started to lag. Analysts are divided about whether Nissan will reach its goal.

Actually, analysts are divided about whether Nissan should reach those goals. Ghosn's targets are controversial because higher sales usually go hand-in-hand with lower profits per car, as manufacturers slash prices to jack up volume. Ghosn has a different take; he figures he won't get anything unless he asks for it. Set the bar too low, and he'll get low-level performance. "Everyone in the company is committed to reaching one million more cars a year," says North American senior vice president Jim Morton. "People want to achieve it for Mr. Ghosn. He pulls the company's image along with him."

With Ghosn spending so much time on North America, he is often asked whether he wants to bring Renault back to the U.S. It has made several attempts to crack that market and failed at all of them. Those with long memories can recall the petite Renault Dauphine that was sold in the 1950s, the quirky Le Car from the 1970s, the Alliance from the 1980s (once known as "the world's first disposable car"), and the fragile Encore. All flopped because of Gallic styling that stressed individuality over utility and comme ci, comme ça reliability. Ghosn is convinced he must reintroduce Renault to the U.S. if he expects its operating profit margin (5.9% in 2004) to catch up to Nissan's (10.2%). But he is a long way from announcing a comeback. "Before coming to market in the U.S., you're going to have to make sure you have good studies, good products, and deep pockets ready to spend billions of dollars," he says. Don't expect to see any Renaults in the U.S. for a good long while.

Ghosn less patiently answers questions about whether he plans to merge the two companies. Though a merger would solve any potential conflict-of-interest problems--one CEO, one group of shareholders--he is convinced that Nissan has thrived because it didn't merge with Renault. Instead the companies have been selectively cherry-picking systems and components from each other. Contrast that with the complications that followed the merger of Chrysler and Daimler-Benz. "I have consistently for the last six years been saying that mergers destroy value," Ghosn says. "What we will do is to continue to strengthen the alliance between the two companies, with an emphasis on saving money through shared purchasing, product development, and engineering." The results of the alliance have been so remarkable to date that Ghosn is under no pressure to further integrate the companies.

The most dramatic savings will come from the sharing of components. Ghosn wants to cut the number of basic mechanical setups the two companies use from 42 in 2000 to just ten in 2010. Last fall Renault launched its first car based on Nissan subcompact models sold in Japan. Built in Romania by Nissan's Dacia unit, the Logan is designed to sell for less than $7,000. Renault will be adding Logan production in Russia, Morocco, Colombia, Iran, and eventually China and hopes to sell some one million a year. If it does, Logan will become the first successful world car sold at entry-level prices.

GHOSN LIKES TO SAY HE would "rather be a pastor in a village than bishop in Rome." But being pastor of two villages with different congregations half a world apart is something else again, and Ghosn admits that he will be stretched. "Taking over as CEO of Renault, I'm going to have my hands full," he says. The measure of his success in both locations, as well as the length of his tenure, will depend on the extent to which he can keep two groups of shareholders happy. Even the Pope might have a difficult time with that.